drm/amd/display: Simplify bool conversion

The result of 'pwr_status == 0' is Boolean, and the question mark
expression is redundant.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=2354
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>